Electromagnetic apparatus.



H. F. STRATTON. ELEQTROMAGNETIC APPARATUS: APPLICATION FILED MAR. 8, I917.

Patented May 8, 1917.

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H. F. STRATTON. ELECTROMAGNETIC APPARATUS.

APPLICATION FIL'ED MAR. 8. I911.

Patented May 8, 1917.

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IN VENTQR. v f/ary IRS/Milan A TTORNEY.

H. F. STRATTON.

ELECTROMAGNETIC APPARATUS.

APPLICATION FILED MAN. 8, I917- Patented May a, 1917;

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Specification of Letters Patent,

Patented May 8,

UNITED STATES PATENTOFFICEQ Original application filed September 9, 1915,'Seria1 No. 49,687; Divided and this application filed finch y 1917. Serial No. 158,887. i i

H jeration of alternatingcurrent motors from standstill to normal running speeds." This invention is a division of my application Serial Number 49,687, filed September 9, 1915. I One object of this invention is to provide for alternating current motors a starting switch which provides a single operating magnet for first connecting the motor to the supply mains through a voltage-reducing means such as a' transformer, and subse-.

quently connecting the motor. directly to the mains; to provide the aforesaid switch with a mechanism which permlts the armature of p the operatingmagnet to move to its full closed positionimmedi'atel upon energiza tionof the magnet, where y the magnet is not left with its. magnetic circuit open while the starting switch is in the Start ing position; to provide a means for releasing the starting switch when in starting position whenever the motor current drops to such a value that it will, on the movement of the switch to the running position, rise to a value substantially equal to the initial value of the current irrespective of the voltage of the starting current; to provide in the apparatus: a mechanism whereby the starting switch, when released, will be automatically removed fromv the starting to the running position by power stored up by the closing movement of the magnet armature;,to provide starting and running contacts, and set of movable contacts for movlng into successive engagement therewith, and cm'istrained by a il'iechanisl'n to move from tl1esta1J'ting position to the run ning position, and thence to a neutral posiupon closurethe shock of impact will be ab sorbed andwill not cause a momentary separation and arcing of the contacts; and to provide astarting magnet for the aforesaid purposes which will be cheap to construct,

Fig. 4, a side elevationflof the switch-opera" ating magnet, and adjacent parts, portions being insection and broken away; Fig. 5,

a partially diagrammatic view of the switch mechanism in neutral position Fig. 6,. a

I view like Fig. 5, except that the switch-mech anism is shown'in the starting position; Fig. 7 a typical diagram of one of several electric circuits which I may employ inconnection with a squirrel-cage motor';.Fig. 8, a diagram of curves illustrating-the use of values; and Fig 9', a section through the pivot 26 and the parts connectedthereby.

On the drawings, 10 designates an oil-' containing casing ortank having the contracted lower portion 10';'bosses 11 being my invention with currents 0f 'difierent i i provided onthe shoulder which connects the r of the casing;

13 is a U-shaped casting constitutingthe main frame for'supporting'the various parts said contracted portion. to the upper portion of my invention. .The'member 1.3" ofthe I frame has the arms 14c,jand"the' other member 13", the'arms 15, thesaid arms havingtheir ends 16 resting on the'bosses 11 and provided with the centering pins 12 fitting in holes in the said bosses. The Tabar 18 is secured .to the upper ends'ofthe members 13* and 13, and constitutes a support by which the frame 13- and the partscarried 7 thereby may be lowered into the casing and removed therefrom. 1 A

'The transformer T, which in the present,

instance is a three-phase auto-transformer with theopen delta coi-ls '19 and 19 and the core 20, is supported by the frame 21 secured I to the under side of the frame 1.3; The coils are each shown with the taps t and theopenf or upper end connections 25'. Thelower ends" the common conl of the coils are connected'to ductor T. M 1

v I'employ a magnet having the Ushaped secured together by the transverse strips 68 of welding material, the rear strips bein welded also to the plates 69 which are bolte' to the inner face of the member 13. The spool has preferably integral therewith the legs 74 bolted to the lower plate 69. Its upper side is shown with a slit extending entirely across the same to prevent the induction of currentsin the spool. 75 .is' a spacing rod'of fiber or other'msulating material seated in grooves in opposite walls of the said slit to maintain the slit at the desired width.

To prevent the chattering of the armature 24 on the'upp'er pole of the magnet, I embed a portion of a closed conductor or loop in the face of-the said pole. This conductor com rises two members, one a strip of metal 0 resting on the support 72 and having its intermediate portion embedded as describedand its end portions bolted to the second member 7 1, preferably a corrugated casting which introduces a resistance into the closed loop and'radiates heat produced in the loop by currents induced therein by the alternating flux in the upper pole piece and generatedby the winding 0 which is connectedby the switch S across two of the line conductors L. The flux induced in the upper pole by the loop alternates with 'the'fiux produced by the windingO, whereby the said pole continuouslyiholds the armature 24 against it. g

The armature 24 is welded by the transverse strips'68 to the upstanding member of the lever 25 pivoted between its ends on the pin 26, which fitsloosely in the lever whereby-the pin will not interfere with any movements of the lever required to make the armature fit squarely on' the upper pole of the magnet and squarely on the plate 77 held loosely between the armature and the lower pole of the magnet; This plate has at its ends holes to receive the two studs '76 projecting from the face of the spool'-23, the holes being slightly larger than 'the' studs in orderthat the plate may adjust itself so as to rest squarely a-gainst the lower pole. The studs 76 have'th'e cotter pins 78to keep the plates from slidingofl' therefrom.v The plate 77-is madeofwearing-resisting, nonmagnetic material having 'high resistance, such as nickel steel." It serves to maintain a non-magnetic gap to prevent the-arma+ ture' from*sticking to the lo'wer pole when thewinding Ois deenergized; The'high resistance of theplate prevents excessive-heating; by eddy currents; 4 he pin 26-is supported by the base of the frame 13 belowethe" armature 24,"and is prefefably composed of non-magnetizable 3, U; y r

material to reduce the flux flowing through the pivotal connection between the frame 13 and the lever 25.

The lever 25 carries above the pivot 26 the horizontal pivot pin 27 on which the upwardly-extending movable switch member 28'and the upwardly-extending stoparm are mounted to swing. The stop-arm 29 carries the pivot 30 to which one end of the link 31 is connected, the other end thereof being connected to one end of the link 32 by the pivot pin 34. The other end of the link 32 is connected to the pivot pin 33 supported by the member 13 of the frame 13. a The links 31and =32 constitute toggle .members, their connecting'pivot 34 being beneath a line connecting their end pivots 30and33;

The pivot 34 supports the depending upper compression member 35. A spring 36 hasits upper end seated on the lower end of the compression member 35,'and its lower endonthe upper face 'of the lower com pression member 37, which isprovided with a centering core 36' for the spring, the two compression members 35 and 37 being kept in ali'nement with the axial center of'the spring 36 by the stem 36, carried by the member 35 and slidable in a central opening in the core 36.

Y A bell-crank lever 38 is pivoted on the pin 39 supported by the member 13 near the lower end thereof: One arm of the lever 38 is connected to the lowerarm of the lever 25 by the link 40, while the other arm of the lever 38 is pivoted to the lower end of the compression member 37, the latter having an open pivot-bearing to-faci'litate its removal and replacement. The member 37 is curvedso that when the parts are as in Fig. 5 the upper arm of' the lever 38 will not interfere with the said member.

The upper end of the stop-arm 29 has three stop surfaces 41, 42,43, the surfaces 41 and 42 being on opposite sides of the arm 29. The switch member 28 has a recess 44 between the opposite-side-walls of which the; upper end of the stop-arm 29 moves, the recess being slightly longer than the distance between thestop surfaces 41 and 42, whereby there exists some lost motion between the members 28'and 29, the switch member 28 having a small angular movement on thepivot 27 independently of the stop-armv 29. The stop surface 43 is adapted torest' on the stop 45 on'the armature lever25. r-

. '46 is a preferably non-magnetic stopon the frame 13 to support the armature lever 25 when in its neutral position, as shown on Fig. 5.

48 is a'latch pivoted between its ends on the'pin 47 supported by the member 13". The lower end of the link 32 has a notch 49 adaptedto be caught by a hook, on the upper side of one end of the latch so as to prevent the straightening of the toggle members 31 and 32 by the spring 36 until they are released by the latch. The other end of the latch lies over the upper end of a two-coil tripping device 50, having the movable core 51, separated from a fixed core in the uppercoil V by the air-gap 52, and from the adjustable core 67 in the lower coil C by the air-gap 53. These coils exert opposite pulls on the core 51. Under certain conditions, to be explained presently, the pull at the gap 52 prepoi'iderates, where upon the core moves upwardly, and the head 54, connected to the core 51 by the rod 55, strikes the latch 48 and causes the latter to release the link 32 in an evident manner.

The arms 14 and 15 support two slates or other insulating bases 56, theari'ns 14: being provided for this purpose with additional arms 57. These slates carry a group of spring cushioned stationary starting contacts 58, 58, 58", and 58, and a group of similar running contacts 59 and 59. The switch member 28 carries a Wooden or other insulating cross-arm 61., on which groups of contacts 62, 62 62", and 62 are mounted.

With the parts in the neutral position shown on Fi 5, it will be noted that the latch is in 100 ing engagement with the link 32, the spring 36 is in its expanded condition, the armature 24 is in its unattracted or neutral position, and the armature lever 25 rests on the stop 46. These parts assume these positions under the action of gravity and the compression spring 36 when the winding 0 is deenergized. WVhen the winding 0 is energized, the armature 24 is drawn to the core 22 and carries the lever 25 with it. The latch 48 prevents any movement of the toggle member 32, so that, as the pivot 27 moves forward with the lever 25, the arm 29 swings on the pivot 30, causing the .end of the arm 28above the pivot 30 to move toward the starting contacts and finally to move the contacts 62, 62, 62, and 62 into engagement with the said starting contacts, as shown on Fig. 6. While the operation just described is taking place, the lever 25 has, through the link 40, turned the bell-crank lever 38 from the position shown on Fig. 5 to that shown on Fig. 6, the lower arm of the lever 38 moving upwardly from its neutral or idle position below its pivot 30 so as to cause the spring 36 to be cmnpressed between the compression members 35 and 37 The parts will. remain as in Fig. 6 until the tripping device 50 operates to release the latch 48, whereupon the spring 36 will cause the toggle members 31 and 32 to be extended and the switch member 28 to be moved into the position shown on F g. 1, in which the movable contacts 62" and 62 are shown in engagement with the running contacts 59 and 59,

respectively, and the said movable'contacts are shown disconnected from the'starting contacts. The parts will remain in this po sition until the winding 0 is deenergized,

y when they will return to the neutral position shown on Fig. 5.

. The blow of the movable contacts 62 upon I the starting or the running contacts, causes the latter to overtravel a slight distance. If a the movable contacts came inflexibly into engagement with the starting or running contacts, this overtravel of the latter would cause a momentary opening of the electrical circuits established by the engagement of the movable and the starting or running contacts. To prevent this momentary interruption of the circuits, I provide sufficient lo'st motion between the stop arm 29 and the movable switch member 28 to which the movable contacts are rigidly connectedfso that the latter may follow the starting or running contacts in their overtravel and may thereby maintain continuous contact with the starting or running contacts as long as the movable contacts are'in the starting or running position respectively. It will be understood that-the overtravel of the starting or running contacts and the coiirdinating follow-up of the movable contacts are but momentary and that both contacts rapidly assume their normal positions under the in uence of the cushioned springs which cooperate with the starting or running contacts.

Onthe casing 10 is a row of terminals 63, 63, 63, 63, 63, and 63. The motor lead M and the contact 62 are connected. to the terminal 63 The motor leads M and M are connected to the terminals 63 and 63 respectively. The terminals 63 and 63 are connected together by the wire N. The contacts 59 and 62 are connected to the terminal 63 andthe contacts 62 and 59 to the terminal 63. The three-phase supply mains L, L", and L are connected to the terminals 63, 63, and 63", respectively. The winding O has one end connected to the terminal 63 1 and the other end to the terminal 63 through the master switch S. The motor is indicated by the letter M and is of the squirrel-cage type with, star-connected stator windings, but I do not limit myself to any definite type of motor or any definite ar- V is ener ized by the secondary voltage of the trans ormer and not by the line voltage, and that the voltage on the coil V will automatically be changed when the transformer taps are adjusted to change the motor starting voltage. The voltage coil V has, preferably in series therewith, the non-inductive high resistance H, which is designed to prevent a high current transient, which might occur in the said coil when first excited, from exerting a sufficiently large pull across the gap 52 to lift the core 51 and trip the latch 48 prematurely.

The four taps t to the winding 19 of the transformer T are connected to the four outer terminals 66 at one end of the block 64, and the four taps t to the winding 19 of the transformer are connected to the four outer terminals 66*v at the other end of the said block. The open ends of-thewindings 19 and 19 are connected by the wires t to the two inner terminals 66 and 66, the latter being connected respectively to the contacts 58 and 58 by the flexible conductors t and t The flexible tap-connector F has one end connected to the terminal 65, its other end being removably connected to any selected one of the four outer terminals 66, and the flexible tap-connector F has one end connected to the terminal 65 and its other end detachably connected to any selected one of the four outer terminals 66". The terminal 65 is connected to the contact 58 by the flexible conductor 2?, and the terminal 65 is connected to the contact 58 by the flexible conductor t The terminals 66 and 66 are preferably above the level of the oil in the tank, so that the tap connectors F and F maybe changed at will to suitably selected terminals 66 and 66 without removing the apparatus from the oil. I

Suppose the parts to be in their neutral positions, as shown on Figs. 5 and 7. To start the motor M the switch S is closed, causing the winding 0 to be energized and the parts to be moved, as already described, to the starting position shown on Fig. 6, in which the contacts 62, 62, 62 and 62 are in engagement with the starting contacts 58, 58 ,58", and 58", respectively. In this position the supply main L is connected through the contacts 62 and 58 to the open terminal of the transformer winding 19*, and the supply main D is connected through the contacts 62 and 58 to the open end of the winding 19, the supply main L being always connected to the remaining ends of the transformer windings irrespective of the starting switch contacts. The motor lead M is connected to the second terminal 66 through the contacts 62 and 58, the current coil C and the tap-connector F. The motor lead M is connected to the second terminal 66 through the contacts 62 and 58 and the tap-connector F", the motor lead speed. When the winding 0 is deenergized M being always connected to the common point T through the conductor N. Thus,

only a portion of the transformer is connected to the motor leads M and M, causing the motor to start under a voltage less than the line voltage. For any given connection of the tap connectors F and F with the tap terminals 66 and 66, the upward pull of the coil V on the core 51 remains practically unchanged for the same line voltage, but the downward pull on the core varies with the current through the motor. When the switch member 28 is first moved into starting position, the rush of current in the coil C causes the downward pull on the core 51 to overpower the upward pull thereon caused by the current in the coil V. When the motor current decreases to such a value that the pull produced by the coil 0 is overpowered by the pull produced by the coil V, the latch 48 is tripped in the manner hereinbefore explained, and the parts move to the running position (Fig. 1),in which the supply main L is connected directly to the motor lead M through the contacts 59 and 62, and the supply main L is connected directly to the motor lead M through the contacts 59 and 62, the supply main L being connected to the motor lead M through the conductor N. The transformer and the coils C and V are disconnected from the supply mains L and L", and the full voltage of the source of current supply is impressed on the motor, whereby the motor is quickly accelerated to running the switch member 28 quickly assumes its neutral position shown on Fig. 5, with the latch 48 in looking engagement with the toggle member 32.

The length of the gap 53 may be adjusted by screwing the plug up or down in the bottom member f of the E-shaped magnetizablc frame which supports the windings C and V and constitutes portions of the magnetic circuits. I adjust the gap 53 so that the pull produced by the coil V will overcome the pull produced by the coil C when the motor current is reduced to such a value that the closing of the running contacts will cause the current to rise to the initial value, that is,'to the value of the current impressed on the motor at the instant the starting contacts are closed. The ampere turns of the coils and V are relatively so proportioned that the magnetic circuit of the coil C is energized at higher degrees of magnetization than that of the coil V, and the adjustment just described is made when the tap connectors F and F are on that part of tap terminals 66 and 66 which give the lowest motor starting voltage. hen the tap connections are changed to give higher starting voltages, the magnetic flux of the coil V will increase approximately in mass? proportion to the voltage, but the flux of the coil C will not be increased in proportion .to.

the motor current at the higher voltage because the magnetic circuit of the coil C is more nearly saturated than that of the coil .V. It will thus beseen that as the starting voltage is ad'usted the ratio between the voltage and t e current at which the trip- 1 ping device 50 operates, will decrease asthe e I voltage, asfvoltage A, the initial current vice will operate to cause the ve acoeleratin current peaks" to bs tan tially equa while constant voltage "1' .being startin voltage 1s increased' When the ga 53 of t e trip device 50 has been adjuste as just described, with the tapconnectors F and F on one pair of tap terminals 66 and 66, no adjustment is required to adapt it to changes of voltage and current values caused by connecting the tap-connectorsto any other pair of tap terminals. This im portant characteristic of m invention is graphically illustrated on F1g. 8, in which the" three'curves in solid lines indicate the current flowing through the motor, during its acceleration withthree difi'e'rent', voltages impressed on the motor. If the motor is started on voltageB and initial current ob, the trip device 50,.operates'to trip the latch 48 so that, whenthe transition to full line voltage occurs, the current through the motor Wlll rise to its initial value 0b. The line b 6* is drawn parallel to the line 0 0'', its end b" meetin the line voltage curve. The line 0' 6 is awn parallel to the line 0 b. The line drawn from o to the intersection bjfof the line o b" with the curve for'volb age B, Y obviously. represents the current voltage should occur.

If the tap connectors F and F be ehanged so as to start'the motor on a higher through the motor willbe om-and the transition. to full line voltage will take'place when the current. drops 'to the" value o a'-,

thefpoint a being at the intersection; of the curve for voltagenA with the line 69 m, arallel with the line 0 a, the polnt'a" j be1ng m the curve for line voltage. ,ThB ti'lPQG- impressed Ton them t g The, pea for voltageA will be higher than for volta e B,fbu't if the windingsvi'o'f the coils. C and I e are proportioned properly the peaks" for voltage A will be approximately equalj to each-other and those for volta' ejB w1ll also beapproximately equal to eac other, I do not l mit myself tov the ideal theoretical ner'that progressively v occur at transition w1th t e useofprogres ,sively, hi herstarting voltages. Although I, have, or simplicity desc'rlb'ed only the operation just given, as in practieeitmay sometimes befpreferable not tofhave equality of current peaks as described, but merelylto cause the transition to occur in such amanvalue at which the transition to fullline hi her currents" will,"

ideal theoretical operation having equality of current peaks, my invention broadly comprises all, means forincreasing automatically and self-adjustably the, current peaks at the transition toline voltage when higher starting voltages are employed. i a

The described coerdinated' 3. mechanism permits the armature 24 to close thejmagnetic circuit of the operatingmagnetimmediately upon energization, thereby preventing the waste ofthe largewattage and the probable destruction of the winding 0 c by overheating, which would occur if the closure of, the said magnetic circuit should be delayed until the running contacts are closed. The said mechanism also causes the l hardest work of the operating/magnet to come at the time when t e gaps between the armature and the poles of the, magnet have become short and, therefore, when-the mag: netic pull on the. armature has approximated its maximum. From Fig.5 it is seen that, during the earliest partof the movement of the armature 24 toward the poles of the magnet, the armature has to the switch member 28 andithe arm 29 .on

their pivot 27 to the positions shown'on Fig. '6, which requires but little power. At

. the same. time the lever 25moves'thelower arm of the lever 38 on nearlya horizontal line, whereby the spring 36is only slightly compressed. After'the'contactsf58 and 62 have en aged each other. and the lower arm ofjthe I ever 38 begins to move'upwardly rapidly,,the armature 24 has moved so close to, the poles of the operating magnet that.

reat power,

it is drawn'to the same with causing the spring 36 to be p aced under high compressiomfcapable of quickly extendingthe toggle members and moving the parts to theflrunnlng. positionshown on Fig;

1, as soon as the trip device '50' releases the latch 48' from the toggle member 32. The arrangement of the moving parts is such" that, at the'beginning of the move ment of the movable contacts from their startin Yto their running position, thefrotativee ortj about the pin 27, due m the s ring" 36, is

relatively small, but toward the end of said movement and practically during engagementv with the running contacts, the rotative effort of the sprin 36, acting member128,throug the togg e levers arena 32, is a maximum. Suchade'sign permits" the employment ofa springon which minimum compressive. efiort 1s required, and:

he use of a smaller and "cheaper; operating magnet. .1 ,5 I

fThe movement of the parts 'fronifjtheir' a 12a leads directly to starting position to their runnin 'po it qn causes the running contacts 59 an 59",tobe' moved back from theiridlepositiom there- 5 i on the switch by .placingtheir springs 60 under, compres sion. The springs 60, reacting through the various parts of the mechanism, to' ao move the lower end of the armature about the upper pole of the magnet as a center, toward the lower pole thereof to prevent chattering, the loose fit of the lever25. on its pivot 26, and of the spacer 77- on its supporting studs 76 permitting the armature to move freely so that it may fit squarel against the upper pole and the plate 7;.

The movable contacts have a plurality of centers of rotation, which permit the armature to move at once to its closed position and at the sametime permit the contacts 62 to 62 to be moved first to the starting position and subsequently to the running position. The contacts 62 to 62 do not, owing to the said centers of rotation, travel on a single line from their neutral position to their starting and runnin positions, and back'to their neutral p0 Sit1OI1, biit describe a, triangular path asshown by the dotted lines near the top of 6, where the neutral, starting, and running positions are indicated, respectively, by the letters N, S, and R, the arrow heads showing the direction of travel. I I

While I have shown my invention in connection with apparatus for starting squirrelcage motors, i is obviousthatflsomeof the principles thereof may be applied to direct current apparatus and to alternating current motors controlled by diiferent voltagecontrolling means from those shown. I do not limit myself to the use of three; base source of supply" or to the squirre figs type of motor. While have shown a traction magnet consisting of a two-pole stationary electromagnet and a piyoted arm ture arranged to be attracted thereto asthe source of mechanical power; for operating ,my invention, it will be apparent that manual means or other types of electromagnetic means capable of developing mechanicalpower and cooperating with the me hanism which I have shown, or'with olier forins of mechanism, -ma'y be eln'l lloyeid s without departing from the spirit ofmy inventi0n.

Iclaini V t 1. In an electro1nagnet', a plurality o?! poles, a loosely pivoted armature arrangedto be attracted thereto, a winding surrol'lndifng one pole, a loosely su ported nonmagnetic V separator between sai pole and the armature, meansproviding a contihlions pulI be tween a second pole and the armature when the winding is energized with alternating current, and externalmeans causing a thrust of the armature against the pole not having poles, a loosely pivoted armature arranged ,Biw

armaturaqfians proyiding a continuous pull between a second ole and the armature whenthe winding is energized with alternating'f current, and external means causing a thrust of the armature ag poles, a loosely pivoted arniature arranged to be attracted thereto against a working load, a winding surrounding one pole, a loosely supported rioli-ma rietic separator between said pole andlthearinature, means providing a continuous pull between a sec ond pole and armature when the winding is energized with alternatingcu rrent, means between the working load an the armature whereby the direction and p q t r appli atioi of the load' tends to separate the armatur i is ed 1 a d t www h arl'i a'ture aware the rse pble on the second pole asa fulcrum an: n p0 es, aflooselyj piyote aw 'aet 1v i erates 8, a d n has P 1 a may urge; .fl t-Ja m e spam: btweeri? 1 p let dm e anfiat'ur mealsri vid h a i' 1 9us'Piil 'i en o'nd pole andt e armature w en the windin I S s fi iz df. .v i wa e i tim .Q Q an means between th working lbad and rainst v a working point 0' application of t he' dad tends to s a'rate the armature frornthe cond' pole d to t l th a 'xila t 'a rd hefi st pie oil-the Tess cru n the secis o p t fis i d ip f p hap w o a i W In" e' lj t ms fll lu a ty of r at an we; x .a i tr i arrange o be aftti acted an energizin g winding for at: stationa'ry pole's, a looseiy supportednonfi Water. i 'eefione po n means providi' a. continuous fl a stai p i he armat e 19 n. in Meir and when the armature engages tfififihc fid r l 190864 P o cq e tionfo'r thl ari'natlire whereon the armature flt p y'rh n et mt t ar the ta: t1'on aiypo1e'sjand whereby the amature ny ar mq ment, t we m f q v he first pole withplitdisngagi the armature filbfil thi 6 Pe e a 6. In. an eliebtroniagnet Emmi atd intei n'iediate of the t pl al ty i was drt amaud w e' f hj wi -T;

pivot fdr t e armature whereon the armam is energised with await ng current, a"

time may rotate toward the poles when attracted thereto and' a lost motion connection between the armature and the pivot whereby after said rotation the armature may have 5 a limited rotary movement toward and from the first pole 0n the second pole as a pivot. 7. An alternating current magnet having a core and an armature, two working gaps between said coreand armature, means 1n o -one gap for producing a continuous magnetic pull therein when the magnet is energized, an energizing winding for the magnet, a spool for the winding a, spacer made of material having highelecrical resistance 15 andlow magnetic permeability loosely supported upon the 'spool in the other gap the a core and an armature, two working-gaps between said core'and armature,'means 1n .one gap for producing a continuous magnetic pull therein when the magnet is energi'zed, an energizing winding for the magnet, anda spacer made of non-magnetic material loosely supported in the other gap, the

armature belng adapted to move toward the:

core and strike upon -the spacer.

Signed at-Oleveland, Ohio, this 5th day of March, AL D. 1917. 3

HARRY 1 SiRATTON. 

